Introduction of polycarboxylate superplasticizers
Classification of polycarboxylate superplasticizers
In the process of rapid economic development and technological development in China, polycarboxylic acid water reducing agent with high efficient water reducing performance is often used in construction concrete. The common ones are: polypropylene hydrochloride, methyl propionic acid, maleic acid polymer, polymaleic acid and so on. Polypropylene hydrochloride water reducing agent integrates well with other types of cement in the process of use and is widely used in the cement field. Actual use process. In the process of use, the monomer acrylic acid is used as a precursor, and polyoxymethylene is chemically combined with polyoxymethylene to obtain a higher molecular weight product. Methylpropionic acid/maleic acid polymer is a block type water reducing polymer formed with methylpropionic acid and maleic anhydride as monomers, and its performance is ensured by compounding with other water reducing agents. Flowability and Adsorption. Maleic acid is a water insoluble polymer reactive granular water reducing agent. Groups such as anhydride and molecular lactone are present in the main chain of the molecular structure. For fresh concrete, the alkaline component will hydrolyse these molecular groups, effectively converting the water-insoluble polymer into a soluble polymer, and at the same time, due to the role of the dispersant, the soluble polymer can slowly enter the solution. Hydrolysis of the concrete surface occurs gradually and slowly, and the slow dispersion effectively avoids slump loss in the concrete structure.
2. Key technologies for using the highly effective water-reducing agent polycarboxylic acid.
In recent years, polycarboxylate superplasticizers have been widely used in many construction projects in my country. Modern concrete places high demands on external functional additives, therefore, when introducing polycarboxylate water-reducing additives into concrete systems, the following key technologies should be taken into account.
(1) Polycarboxylic acid system compatibility technology. Due to the special structure of the highly effective polycarboxylic acid water-reducing agent, it cannot be stored and used together with other water-reducing agents, especially naphthalene-based water-reducing agents. If it is necessary to alternately use different types of highly effective superplasticizers, the corresponding containers must be thoroughly cleaned so that cross-contamination does not affect the quality of the concrete. The adsorption properties of high-performance superplasticizers vary depending on the type of cement. Since the compatibility range of polycarboxylate superplasticizer with cement is relatively narrow, poor compatibility is inevitable. Therefore, it is necessary to increase its dosage or use a different type of cement. to effectively solve this problem.
⑵Polycarboxylate water-reducing agent technology. In the construction process, due to the short deceleration time, the use of retarder can effectively prolong the ductility of concrete. However, the incompatibility between them should also be taken into account to avoid reducing the performance of concrete.
⑶Gas control. The polycarboxylate water-reducing agent has a good air-entraining effect and can be used in conjunction with defoamers and air-entraining agents. By first eliminating it and then introducing it, the air content of the concrete can be controlled, improving its workability and durability.
⑷Control of dirt content in sand and gravel. The dirt content of sand and gravel also affects the effectiveness of the polycarboxylate high-performance water-reducing agent. If the silt content of the sand exceeds 2%, the structure between the clay layers will absorb a large number of water-reducing agent molecules, thereby reducing the flowability of the concrete. If the mud content during construction is relatively high, the use of a clay-resistant polycarboxylate superplasticizer should be considered.